How to calibrate an electrochemical gas sensor?

If you own an electrochemical sensor, you should know that calibrating an electrochemical sensor can make a difference between night and day. An electrochemical sensor that is not calibrated correctly will give you incorrect readings.

Calibration is the process of matching a sensor’s output to a known standard. If the two readings match, then the sensor is "calibrated," and if they don't, it isn't.

This article will enlighten you with simple information with which you should be able to calibrate your electrochemical sensor on your own and make it work accurately.

A sensor can be calibrated in many ways.

1. Span (2-point) calibration

2. Single point calibration

3. Automatic Background Calibration

Span Calibration

The manufacturer mostly performs this calibration at the factory right after the production of the sensor. The sensor is exposed to two types of gases, the first with no target gas and the second with a known amount of target gas.

For the first step, the sensor is exposed to inert gas like nitrogen or argon with zero amount of the target gas. For example, if a sensor is made to detect oxygen or carbon monoxide gas, it will give a zero percent reading for it, and this reading will be stored in the memory chip of the sensor.

In the second step, the sensor is exposed to a known amount of target gas. Usually, the highest amount the sensor is rated to test. A 20 percent carbon monoxide sensor is exposed to 20 percent carbon monoxide gas, and again this reading is saved in the sensor's memory.

Once these two readings are stored on the sensor, the sensor can detect a linear response to the gas concentration between the two points. Some sensors can not accurately detect a gas concentration using two-point calibration, so the manufacturers add more points and four-point calibration.

Single point calibration

This type of calibration is done in the sensors in which total cost is more important than maximum accuracy. It is used once only a single measurement point of gas is needed.

Mostly single-point calibration is done in the open and fresh air, which has 78% oxygen, 21 % oxygen, and all other gases are in fairly smaller amounts. The sensor detects the deviation from these standard amounts because all these ratings are recorded and stored on the sensor.

Automatic background calibration

It is known as automatic background calibration, but it is an automated form of single-point calibration in reality.

The reason behind this calibration is that it was expensive and required trained staff to take off the wall-mounted sensors in buildings and calibrate them. In Automated background calibration (ABC), the lowest rating of the target gas is stored in the memory chip of the sensor, and any deviation from this rating is then calculated against it.

For maximized accuracy, the devices that use ABC should be calibrated manually over time. It has a disadvantage that the sensor is more likely to display inaccurate levels of the target gas.

These are the three major ways that you can use to calibrate your electrochemical gas sensor based on the gas that you are dealing with and the amount of accuracy you want to achieve.